1. Field of the Invention
The invention pertains to translucent web-type recording material, which comprises a substrate; a recording layer on at least one side of the substrate, to which data can be recorded; and pigmented marking between the substrate and the recording layer. The invention also pertains to a process for the production of the recording material according to the invention.
2. Description of Prior Art
Recording materials are essential to daily life in society and to the working world. Recording materials which are to be used only by authorized persons are usually provided with a specific marking, which indicates that the material is approved for this purpose. Various solutions for providing security features which can prove the authenticity of copy materials have already been proposed in the past.
Watermarks, for example, make it possible to prove the authenticity of documents by means of a passive examination. A watermark is generally understood to be an image formed in the paper by altering the thickness of the paper in the appropriate areas. A distinction is made between true watermarks, half-true watermarks, and false watermarks. True watermarks are produced by decreasing the density of the pulp (so-called “translucent” watermarks) or by increasing the density of the pulp by the use, for example, of a dandy roll in the screen section of the paper machine (so-called “shadow watermarks”). Half-true or so-called “molette” watermarks are produced by impressing the paper in the pressing section of the paper machine while the paper is still wet. Finally, there are the false watermarks which are produced either by printing the finished paper with a colorless coating material outside the paper machine or by embossing the finished paper outside the paper machine.
Proposals for false watermarks can be found in EP 0 203 499 B 1, which provides a paper web, which, as a result of the addition of suitable substances, can be deformed by the application of heat and possibly by the simultaneous application of pressure, and in DE 39 20 378 A1, according to which a watermark is produced outside the paper machine by printing the paper with a coating material. The disadvantages of these proposals is that their realization is limited to only certain areas of application because of the need for expensive raw materials.
According to a proposal of DE 690 01 677 T2, a synthetic print carrier with false watermarks is made available. This known print carrier comprises a substrate made of plastic; at least one authentication or security symbol, which is preferably applied by intaglio printing and which changes the opacity of the print carrier; and at least one pigment coating, which can be printed onto the carrier to cover the symbol. The monochrome or polychrome symbol is said to be almost invisible in reflected light but readily visible in transmitted light. The basic disadvantage, namely, that a printed false watermark can be forged relatively easily, also applies to this known print carrier; forgery cannot be prevented by the simple pigment coatings applied over the mark.
As a first security feature in the form of a false watermark for a heat-sensitive copy material, EP 0 844 097 A1 discloses a latent image printed on the back of the recording material. This image is produced by means of a security ink containing a fluorescent reagent. To create a second security feature in the form of a waterproof image on the back of the heat-sensitive recording material, the security ink contains a water-repellent material. The fluorescent reagent used as pigment or dye and the security ink containing the water-repelling agent are contained or dispersed in an aqueous carrier, which can also contain a binder in addition to these components. The disadvantage of this proposal is that the water-repelling character of the security ink makes it more difficult to arrange preprints by the conventional printing methods as often done in practice. Preprints are form fields, produced by offset printing, for example, which are intended to be filled out later by a thermal printer, for example.
Another disadvantage of basically all false watermarks is to be found in the fact that they are applied afterwards to the finished paper by embossing or printing, for which reason it is easier to forge them than it is to forge true or half-true watermarks or even those types of watermark-like security marks which are integrated into the structure of the recording paper during the production process. The closer the creation of a safety feature to the original production point in the production and processing chain, the greater the difficulty of simulating the safety feature with the intent of forgery.
A true watermark made in the substrate of web-like recording material provided with a heat-sensitive coating is known from EP 0 611 664 B1. This watermark cannot always be detected satisfactorily in transmitted daylight, however, which makes the identification process more difficult. In addition, the devices required for production, such as customized dandy rolls, are very expensive.